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Visible light communication (VLC) has become a promising technology for high data rate communications and an attractive complementary to conventional radio frequency (RF) communication. VLC is a secure, energy efficient and cost-effective technology that exploits the existing infrastructure, particularly in indoor environments, for wireless data transmission. Nevertheless, the main limitation of developing high data rate VLC links is the narrow modulation bandwidth of light-emitting diodes (LEDs), which is in the megahertz range. The power domain nonorthogonal multiple access (PD-NOMA) scheme is envisioned to address several challenges in VLC systems. In this paper, we present a detailed overview of PD-NOMA based VLC systems. Moreover, we introduce insights on some PD-NOMA VLC system constraints and challenges such as power allocation, clipping effect, MIMO and security. Finally, we provide open research problems as well as possible directions for future research to pave the way for the implementation of PD-NOMA VLC systems.

In recent times, nonorthogonal multiple access (NOMA) has appeared as an encouraging system for satisfying the requirements of 5G communications in alleviating the spectrum insufficiency problems. The purpose of NOMA in heterogeneous networks (HetNets) is to increase the spectrum exploitation with the cost of proficient allotment of resources. Therefore, to achieve effective resource assignments for NOMA HetNets, this study develops the best user pairing and efficient power allocation approach. Here, the newly devised optimization method, Feedback Sea Lion Optimization (FSLnO), is employed for achieving a less-difficult optimal solution when user pairing. In addition, the designed FSLnO is also accomplished for performing the energy-efficient power allocation process by enhancing the lesser energy effectiveness of the femtocell users. The Feedback Artificial Tree (FAT) and Sea Lion Optimization (SLnO) are combined to create the developed FSLnO algorithm. Additionally, according to evaluation metrics like achievable rate, energy efficiency, sum rate, and throughput, the developed approach performed better, with maximum values of 2.384 Mbits/s, 0.028 Mbits/Joules, 13.27 5 Mbits/s, and 0.154 Mbps, respectively.

Generalized Singular Value Decomposition (GSVD) is the enabling linear precoding scheme for multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems. In this paper, we extend research concerning downlink MIMO-NOMA systems with GSVD to cover bit error rate (BER) performance and to derive an approximate evaluation of the average BER performance. Specifically, we deploy, at the base station, the well-known technique of joint-modulation to generate NOMA symbols and joint maximum-likelihood (ML) to recover the transmitted data at end user locations. Consequently, the joint ML detector offers almost the same performance, in terms of average BER as ideal successive interference cancellation. Next, we also investigate BER performance of other precoding schemes, such as zero-forcing, block diagonalization, and simultaneous triangularization, comparing them with GSVD. Furthermore, BER performance is verified in different configurations in relation to the number of antennas. In cases where the number of transmit antennas is greater than twice the number of receive antennas, average BER performance is superior.

The massive connectivity requirement and security issues have become major factors restricting the further development of the Internet of Things. Nonorthogonal multiple access (NOMA) can be combined with physical layer security (PLS) to achieve massive connectivity and secure transmission. This article investigates the PLS performance for a downlink communication system over Nakagami-m fading channels, with full-duplex (FD) cooperative NOMA transmission aided by artificial noise (AN). While direct communication is built between the base station and two NOMA users, the strong user is employed as an FD relay as well as the jammer to enhance the PLS of the legitimate transmission in the presence of a passive eavesdropper (Eve). Closed-form analytical expressions in terms of the outage probability of the legitimate users and the intercept probability of Eve are derived to evaluate the security–reliability trade-off (SRT) of the proposed scheme. Monte Carlo simulations are provided to validate the veracity of the theoretic analyses and illustrate that the proposed scheme is superior in terms of SRT to the benchmark schemes in the low SNR region. Furthermore, the results reveal that the SRT performance of the two NOMA users can be enhanced through a proper AN-bearing ratio and power allocation optimization.

As an important port technology in mobile communication, multiple access can effectively improve the number of user access in the communication system. However, the Orthogonal Multiple Access (OMA) technology has been unable to meet the higher requirements of spectrum efficiency and system capacity in the future, so it is of great practical significance to study and design a new multiple access technology. Sparse Code Multiple Access (SCMA), as a new non-orthogonal multiple Access (NOMA) scheme, improves the number of user access and spectrum utilization by superposition of multi-user information on the same time-frequency resource. And it can well adapt to all kinds of new application scenarios in 5G. This paper introduces SCMA technology from four aspects: basic principle, system model, key technology and its combination with other systems.

Space-division multiple access (SDMA) utilizes linear precoding to separate users in the spatial domain and relies on fully treating any residual multi-user interference as noise. Non-orthogonal multiple access (NOMA) uses linearly precoded superposition coding with successive interference cancellation (SIC) to superpose users in the power domain and relies on user grouping and ordering to enforce some users to fully decode and cancel interference created by other users.In this paper, we argue that to efficiently cope with the high throughput, heterogeneity of quality of service (QoS), and massive connectivity requirements of future multi-antenna wireless networks, multiple access design needs to depart from those two extreme interference management strategies, namely fully treat interference as noise (as in SDMA) and fully decode interference (as in NOMA).Considering a multiple-input single-output broadcast channel, we develop a novel multiple access framework, called rate-splitting multiple access (RSMA). RSMA is a more general and more powerful multiple access for downlink multi-antenna systems that contains SDMA and NOMA as special cases. RSMA relies on linearly precoded rate-splitting with SIC to decode part of the interference and treat the remaining part of the interference as noise. This capability of RSMA to partially decode interference and partially treat interference as noise enables to softly bridge the two extremes of fully decoding interference and treating interference as noise and provides room for rate and QoS enhancements and complexity reduction.The three multiple access schemes are compared, and extensive numerical results show that RSMA provides a smooth transition between SDMA and NOMA and outperforms them both in a wide range of network loads (underloaded and overloaded regimes) and user deployments (with a diversity of channel directions, channel strengths, and qualities of channel state information at the transmitter). Moreover, RSMA provides rate and QoS enhancements over NOMA at a lower computational complexity for the transmit scheduler and the receivers (number of SIC layers).

Today’s wireless networks allocate radio resources to users based on the orthogonal multiple access (OMA) principle. However, as the number of users increases, OMA based approaches may not meet the stringent emerging requirements including very high spectral efficiency, very low latency, and massive device connectivity. Nonorthogonal multiple access (NOMA) principle emerges as a solution to improve the spectral efficiency while allowing some degree of multiple access interference at receivers. In this tutorial style paper, we target providing a unified model for NOMA, including uplink and downlink transmissions, along with the extensions to multiple input multiple output and cooperative communication scenarios. Through numerical examples, we compare the performances of OMA and NOMA networks. Implementation aspects and open issues are also detailed.

Thanks to their potentials in providing reliable communications for a large number of devices, 5G non-orthogonal multiple access (NOMA) techniques have recently been the subject of considerable research interest. Accordingly, research of Physical Layer Security approaches in NOMA is essential. A primary purpose and challenge for security at the physical level of NOMA-based systems is to protect the information transmitted against both external and internal eavesdropping attacks. To this end, it is necessary to develop PLS schemes which allow each user to decode the signals transmitted by other users, thus guaranteeing normal operation of the successive interference cancellation, while also providing privacy of the information exchange. In this paper, different types of eavesdropping are studied and a summary of existing approaches to improve security at the physical layer in 5G NOMA networks is provided.

Orthogonal time frequency space (OTFS) and non-orthogonal multiple-access (NOMA) are both wireless transmission technologies suitable for high-speed scenarios. This paper proposes a cross-domain transmission scheme combining OTFS and NOMA applicable to the Internet of vehicles. We establish a channel model of cross-domain transmission. Based on the downlink, we deduce the expression for the SINR of the transmitted signal. We simulate and analyze the spectrum efficiency and other performance from the perspective of the system level. At last, we make a comparison between the OTFS-based NOMA system and the OFDM-based NOMA system. Numerical results manifest that OTFS-NOMA has better performance in terms of outage spectrum efficiency.

Communication networks of future generations should provide a high level of spectral efficiency. The multiple access method is one of the technologies that directly affect this parameter. During the discussion of fifth-generation communication networks, a new approach to designing the non-orthogonal multiple access was proposed. One of the implementation techniques of this approach is sparse code multiple access. In the article, we consider this method and propose an approach to the development of a modulation code scheme to evaluate the sparse code multiple access performance and efficiency under transmission conditions close to reality. The approach is based on a similar modulation code scheme of existing communication systems. To form sparse code multiple access symbols, a codebook based on the mother constellation rotation and interleaving method is considered. We also introduce a modulation code scheme table for SCMA communication systems and evaluate their spectral efficiency.